1. Field of the Invention
The present invention relates to an elevator door control apparatus for controlling by means of an inverter the driving of a motor for opening and closing elevator doors.
2. Description of the Related Art
FIG. 7 shows the mechanical construction of a commonly used elevator door system. In FIG. 7, the elevator door system has a hanger case 4, a door control apparatus 14B fixed to the hanger case 4, a motor 10 for driving the doors, the motor being connected to the door control apparatus 14B, and a driving apparatus 9 provided onto the hanger case 4, in which apparatus a motor 10 is incorporated. A door 1 disposed on a hatchway 2 for a car is coupled to the driving apparatus 9 via a four-throw driving link 11. Disposed in the door 1 is an engagement apparatus 8 which is engaged by an apparatus disposed on a landing-place door (not shown) within a predetermined door zone for making the door 1 of an elevator car ,move in linkage with a landing-place door. Also disposed in the door 1 is a door hanger 3 which moves along a rail 5 by means of hanger rollers 6 and upward thrust rollers 7 so as to guide the opening and closing of the door 1.
A door stopper 14A on the door open side and a door stopper 14 on the door closed side, each of which is made of an elastic body, are disposed in the hanger case 4. Also, an OLT sensor 13 for indicating a door-open state and a CLT sensor 12 for indicating a door-closed state are disposed in the hanger case 4. Furthermore, a door strike metal fitting 14C which strikes door stoppers 14 and 14A, and a metal fitting 14D for causing the OLT sensor 13 and the CLT sensor 12 to be activated are fixed to the door hanger 3.
The circuit diagram of a conventional door control apparatus 14B for controlling the above-described elevator door system is shown in FIG. 8.
A three-phase alternating current or a single-phase alternating current of 200 V or 220 V, for example, which is input from a power source is rectified by a diode bridge 15 and smoothed by a smoothing capacitor 16 to generate a dc voltage. The dc voltage is controlled to obtain a sine-wave motor current by an inverter 17 comprising switching elements such as transistors, FET's or the like. During this control, the switching elements of the inverter 17 are subjected to pulse width modulation by the PWM pulse generated from a PWM pulse generator 19. In this way, the speed and torque of the door driving motor 10 are controlled.
The speed of the door driving motor 10 is detected by an encoder 10A provided on the motor shaft. The speed .omega..sub.r * detected by the encoder 10A is subtracted from the speed command .omega..sub.r generated from a speed command generator 22 in a microcomputer 31 at a first addition point 23 to determine a speed deviation .DELTA..omega..sub.r. The speed deviation .DELTA..omega..sub.r is input to a speed amplifier 24, which calculates torque necessary for the door driving motor 10 in accordance with the speed command .omega..sub.r and inputs to a slip calculating section 26 a torque command, e.g., a current iq corresponding to the torque and a current command id corresponding to excitation, which is generally a constant value within a constant torque region. The slip calculating section 26 generates a slip frequency .omega..sub.s. The slip frequency .omega..sub.s is added to the speed .omega..sub.r * detected by the encoder 10A at a second addition point 27 and then input to a phase counter 28 serving as an integrator. In the phase counter 28, the rotational angle of the driving motor is calculated by the equation, .theta..sub.r =.intg.(.omega..sub.r *.+-..omega..sub.s) dt.
The phase angle .theta..sub.i, which is calculated from the current iq corresponding to the torque and the current command id corresponding to excitation by a phase angle calculating section 30, is added to the rotational angle .theta..sub.r of the magnetic field at a third addition point 29 to determine an actual current phase angle .theta.=.theta..sub.r +.theta..sub.i. From the phase angle .theta. and the current amplitude .vertline.I.vertline. generated from a current amplitude calculating section 25, a current command generating section 21 generates a U-phase current command Iu=.vertline.I.vertline..multidot.sin .theta. and a V-phase current command I.sub.v =.vertline.I.vertline..multidot.sin (.theta.+2/3.pi.). From the current commands and the actual motor currents I.sub.u *, I.sub.v *, which are respectively detected by dc current transformers 18, deviations .DELTA.I.sub.u, .DELTA.I.sub.v and .DELTA.I.sub.w =-.DELTA.I.sub.u -.DELTA.I.sub.v are determined by a DC amplifier 20. A three-phase PWM voltage command corresponding to the three deviation values is generated from a PWM pulse generator 19. The pulse train is supplied to the inverter 17 so as to actuate the switching elements thereof. This permits the current, voltage and frequency of the door driving motor 10 to be respectively controlled to predetermined values. The above-described series of operations control the rotational speed and the torque of the door driving motor 10.
In FIG. 8, reference numeral 32 denotes a power-supply cutoff detector. Reference numeral 33 denotes an abnormality detector which is activated when an excess current of an motor occurs, or a routine of a watch timer for detecting an abnormality of a microcomputer 31 is executed. Reference numeral 34 denotes an OR gate for carrying out the logical OR between the output of the power-supply cutoff detector 32 and the output signal of the abnormality detector 33. Reference numeral 35 denotes a relay driver for outputting a signal indicating that the door control apparatus 14B is operating normally on the basis of the output signal of the OR gate 34.
Next, the operation of the above-described conventional elevator door control apparatus 14B will be explained.
When an input power supply falls below a predetermined voltage or is stopped, the power-supply cutoff detector 32 is activated. The output signal of the detector 32 causes the base of an inverter 17 to be shut off through an OR gate 34, with the result that the current of a door driving motor 10 is cut off. Also, when the abnormality detector 33 is activated by an excess current of a motor or a routine of a watch timer for detecting an abnormality of a microcomputer 31 is executed, the current of the door driving motor 10 is cut off in a manner similar to that described above.
FIG. 9 shows the characteristics of the usual speed of the door 1 when the door is closed. Usually, the speed of the door 1 is accelerated as 0.fwdarw.A.fwdarw.B, reaches a maximum speed, and is decelerated as B.fwdarw.C.fwdarw.D. Suppose that, when the speed of the door 1 reaches near the maximum speed indicated at point B, the input power supply decreases or is stopped, thereby causing the power-supply cutoff detector 32 to be actuated. At this time, as shown by the dashed line in FIG. 9, the door 1 runs freely as B.fwdarw.E from the maximum speed due to its own inertia energy without being braked and strikes the door stopper 14 on the door closed side. For this reason, there has been the problem that when a person is sandwiched in the door 1, the door does not stop or move in reversely, which is very dangerous.